An electronic package is basically an open-top housing for containing one or more circuit components such as a diode, transistor, integrated circuit, etc., and a cover for the housing. A so-called power package is one which is hermetically sealed and able to withstand very high temperatures. In order to provide electrical links between those components and the outside world, electrical feed-throughs or leads are provided in one or more walls of the package housing. The leads have to be hermetically sealed in those walls in order to maintain the integrity of the package. In practice, if there is a failure of the package, i.e. a leak, it usually occurs at one or another of its sealed-in leads. Such failures can be due to external effects such as corrosion at the lead due to the environment, or they may be due to differences in the thermal and/or electrical characteristics of the materials comprising the package itself.
Conventionally, the power package housing is composed of side walls formed integrally as a ring and a flat bottom wall or base which is brazed to the lower edges of the side walls. The side walls may be made of a heat-resistant metal, e.g. molybdenum, tungsten, copper, copper alloy, nickel, iron or its alloys, or a ceramic such as alumina or beryllia. Since the bottom wall or base of the package is usually subjected to the most heat, that wall, although it may also be of metal, is often a flat wafer or plate made of a ceramic material such as alumina or beryllia that is brazed t the lower edges of the side walls. Usually metallic features are printed on the base, or conductive mounting pads are provided there, for mounting the circuit components to be housed in the package. The features and pads may also provide electrical connections for the components, (e.g. a ground plane).
If the package is constructed of two pieces, i.e. a ring-like side wall and flat base, prior to brazing the base to the side walls, leads are installed in one or more of the side walls. For this, the side walls are formed with through-holes for receiving the leads. A glass or ceramic seal is provided in the spaces between the leads and the walls of the holes to mechanically fix the leads and to hermetically seal them to the housing walls. If the package is of one-piece construction, the procedure is the same as above without the need to braze the side wall to the base.
One drawback of prior power packages of this general type is that they have a relatively high rejection rate when installing components in the packages so that their overall manufacturing cost is excessively high. Usually, the rejection occurs because of a failure in the hermetic seal at one or another of the leads. Another frequent failure is glass cracking in the meniscus around the lead which exposes base metal and results in subsequent corrosion problems. The failure rate is usually higher for glass-sealed leads than for ceramic-sealed ones. But for both, the failure of a single such seal means a rejection of the entire housing, or at least the side walls thereof since they are invariably formed integrally as a ring.
Also, prior power packages are relatively heavy either because their housings are made of metal or the integrally formed walls have to be relatively thick in order for the housings to be able to withstand the requisite temperature extremes. While the weight of such a small object may appear, at first glance, to be of not much consequence, in some aerospace applications, many power packages must be used in a single satellite, missile or the like, so that minimizing the weight of each package becomes important.